The present invention relates to a drive system for an electrochromic display containing an electrochromic material held in two electrode carrying support plates, at least one of which is transparent, to manifest reversible variations in the light absorption properties when current is supplied.
The present invention relates, more particularly, to a drive system which can compensate for variations of an output level of a power source in order to stabilize coloration and bleaching operations.
An electrochromic material is one in which the color is changed by the application of an electric field or current. See, for example, L. A. Goodman, "Passive Liquid Display", RCA Report 613258.
There are two types of electrochromic displays (referred to as ECD hereinafter). The first type of ECD includes an inorganic solid film formed on electrodes, which produces color variations by the change in the opacity. The second type of ECD utilizes an electrically induced chemical reduction of a colorless liquid to produce a colored, insoluble film on a cathode surface.
It is known that the degree of the coloration of the ECD is dependent on the total amount of charges passed through a unit area. That is, the degree of the coloration of the ECD increases as the total amount of charges per unit area is increased.
Generally, there are three types of drive techniques for the ECD, that is, the constant-potential type, the constant-voltage type and the constant-current type. In these drive systems, it is required that an output level of a power source be at a fixed predetermined level in order to stabilize the coloration and bleaching operations. However, when the ECD is power supplied by a cell, there is a great possibility that the power source output level varies in a fashion depending on the operational life of the cell.
Accordingly, an object of the present invention is to provide a driver circuit for electrochromic display.
Another object of the present invention is to stabilize coloration and bleaching operation in an electrochromic display.
Still another object of the present invention is to minimize power dissipation in a driver circuit for electrochromic displays.
Yet another object of the present invention is to provide a driver circuit for an electrochromic display which is power supplied by a cell or a battery.
Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
To achieve the above objects, pursuant to an embodiment of the present invention, a constant-voltage circuit is interposed between a power source cell and a driver circuit in order to compensate for variations of an output level of the power source cell. Switching means are interposed between the power source cell and the constant-voltage circuit for placing the constant-voltage circuit in an operative condition only when the coloration operation or the bleaching operation is conducted, thereby minimizing power dissipation.